Biodegradation of poly-3-hydroxybutyrate after soil inoculation with microbial consortium: Soil microbiome and plant responses to the changed environment; DNA sequences

DNA sequence reads from used for metagenomic analysis in the study.

Abstract

Biodegradable plastics can play an important role in solving global plastics disposal problems. Poly-3-hydroxybutyrate (P3HB) is a biodegradable bacterial intracellular storage polymer with a wide usage in agriculture. P3HB and its degradation products are assumed to be non-toxic. However, previous studies suggested that its biodegradation negatively affects plant growth due to their competition with microorganisms for nutrients. A solution of this

issue may hypothetically be the microbial inoculation of soil by the consortium of plant growth-promoting and N-fixing microorganisms. To verify this hypothesis, we carried out a pot experiment with lettuce (Lactuca sativa L. var. capitata L.) grown in soil amended with two doses (1% and 5% w/w) of P3HB and microbial inoculant (MI). Five experimental variants – P3HB 1%, P3HB 1% + MI, P3HB 5%, P3HB 5% + MI, MI – were tested to evaluate the effect of added microorganisms on plant growth and P3HB biodegradation. Efficient P3HB degradation, directly dependent on amended bioplastic dose, was coupled with preferential utilization of P3HB as a C source. Due to a higher demand of conditionally more abundant microbial degraders for nutrients in P3HB-amended soil, respiration and enzyme activities were enhanced, indicating increased mineralization of C as well as N, S, and P. Microbial inoculation provided functionally specific bacterial taxa, which further enhanced degradation efficiency and turnover of the nutrients (N, S, P) in P3HB-amended soil. P3HB-related soil acidification was not determinative for plant growth inhibition. However, plant biomass yield remained limited despite the MI-derived plant growth-promoting rhizobacteria (PGPR) and N2-fixing microorganisms, which were assumed to mitigate P3HB-related plant growth inhibition.